The generation of hydrogen-containing reformate from hydrocarbon fuels, for various purposes such as regeneration of adsorbents used to trap oxides of nitrogen in the exhaust of internal combustion engines, particularly diesel engines, is accomplished in various ways. In a typical system, hydrocarbon fuel is desulfurized and preheated, mixed with air, and passed through some form of reformer, typically a catalytic partial oxidizer, a non-catalytic homogenous partial oxidizer, an auto-thermal reformer, and the like. If reformate is to be utilized, for instance, as fuel for a fuel cell power plant, which produces electricity from hydrogen and oxygen (typically air), the carbon monoxide in the hydrogen-rich gas must be removed because carbon monoxide poisons the fuel cell catalyst.
One type of hydrogen reformate generator known to the prior art is illustrated in FIG. 1. In FIG. 1, a fuel processing system 6 comprises a reformer tower 7 and a preferential CO oxidizer (PrOx) tower 8. In the tower 7, preheated, desulfurized fuel enters an inlet 11 along with humidified air at an inlet 12. The two are combined in a mixer 14 before passing into a catalytic partial oxidizer (CPO) 15. The output of the CPO is mixed in inert packing 16 with water provided at an inlet 17 and sprayed as droplets over the packing by a nozzle 18. The components of the CPO outlet are typically some hydrogen, CO2, CO and a significant amount of unreformed hydrocarbon fuel. Mixing that with water in the inert packing 18 prepares the mix for conversion in a high temperature water/gas shift reactor 20, the output of which is passed through a heat exchanger 21. As is known, the water/gas shift reaction converts water and CO to CO2 and hydrogen. Then, the product is processed again in a low temperature water/gas shift reactor 22 before passing through the outlet 25 of the tower 7 into a mixer 26. The coolant received at an inlet 27, heated within the heat exchanger 21 and passing through an outlet 28 may be utilized, under proper conditions, to preheat the desulfurized fuel.
The flow from the reformer tower 7 has air from an inlet 29 mixed therewith in the mixer 26 and then enters the bottom of the tower 8, first passing through another heat exchanger 30 and then through packs 31 of preferential carbon monoxide oxidizer catalyst. The upward flow is mixed with air from an inlet 32 in a mixer 32a and then flows through another heat exchanger 33 which receives coolant at an inlet 34 and provides coolant at its outlet 35 to an inlet 36 of the heat exchanger 30. The coolant at the outlet 38 of the heat exchanger may be utilized, under proper conditions, for preheating fuel or other purposes in ancillary apparatus, all as is known.
The cooled upward flow is passed through additional packs 40 of preferential carbon monoxide oxidizer catalyst and then through a final heat exchanger 41 that receives coolant at an inlet 42 and provides coolant at an outlet 43, which may be used for heating and related processes. The output from the heat exchanger 41 at an outlet 45 of the oxidizer tower is hydrogen rich reformate with on the order of 100 parts per million of carbon monoxide, in the usual case, along with small amounts of carbon dioxide and trace amounts of other gases, including some unreformed hydrocarbon fuel.
As is known, the fuel for such a device may be natural gas, gasoline, diesel fuel, liquified petroleum gas, and other hydrocarbon fuels.
Problems with the apparatus described with respect to FIG. 1 include insufficient residence time for water droplets in the inert packing 16 to become fully vaporized; un-vaporized water may drain into the shift reactor 20 and damage the shift catalyst therein.
Therefore, less water may be used for safety, and the conversion to hydrogen within the shift reactor 20 may be water-starved and thus leave an excess of carbon monoxide, which may overburden the shift reactor 22.
The up flow in the tower 8 requires the use of packs of captured catalysts, such as by netted mesh, which is not only expensive but upon which sufficient catalyst cannot be wash coated, unless large volume packs are utilized. Stated alternatively, to achieve sufficient wash coat on the catalysts may require a larger volume of catalyst than can be accommodated in the space available in certain applications.
In the production of hydrogen, it has heretofore been known to generate reformate, as described hereinbefore, and separate the hydrogen by means of a pressure swing adsorption system, as shown in U.S. Pat. Nos. 5,961,928 and 6,051,192, which results in a loss of some of the hydrogen during purges, and therefore reduces the efficiency of the process. The hydrogen may thereafter be pressurized, within storage/dispensing containers.